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May 8, 2014

Rising CO2 Lowers Nutrition Value Of Crops

by editor

redOrbit Staff & Wire Reports - Your Universe Online

Grains, legumes and other crops that provide a large percentage of the world with most of their dietary zinc and iron will have dramatically reduced concentrations of those nutrients by 2050 due to rising levels of atmospheric carbon dioxide, according to a new study led by Harvard School of Public Health (HSPH).

The researchers studied multiple varieties of wheat, rice, field peas, soybeans, maize and sorghum grown in fields with atmospheric carbon dioxide levels comparable to those expected in the middle of this century, or about 550 parts per million (current CO2 concentrations are about 400 parts per million).

The teams simulated high CO2 levels in open-air fields using a system called Free Air Concentration Enrichment (FACE), which pumps out, monitors and adjusts ground-level atmospheric CO2 to simulate future conditions. All other growing conditions – sunlight, soil, water, and temperature – were the same for plants grown at high-CO2 and those used as controls.

The results of the study revealed that the nutritional quality of a number of the world's most important crop plants fell in response to elevated CO2 levels.

"When we take all of the FACE experiments we've got around the world, we see that an awful lot of our key crops have lower concentrations of zinc and iron in them (at high CO2)," study author Andrew Leakey, professor of biology at the University of Illinois, told Diana Yates, Life Sciences Editor for the University of Illinois at Urbana-Champaign.

Zinc and iron declined significantly in wheat, rice, field peas and soybeans, while wheat and rice also saw notable declines in protein content at higher CO2, the study revealed.

"Across a diverse set of environments in a number of countries, we see this decrease in quality," Leakey said.

Nutrients in sorghum and maize remained relatively stable at higher CO2 levels because these crops use a type of photosynthesis known as C4, which already concentrates carbon dioxide in their leaves, Leakey said.

"C4 is sort of a fuel-injected photosynthesis that maize and sorghum and millet have.”

"Our previous work here at Illinois has shown that their photosynthesis rates are not stimulated by being at elevated CO2. They already have high CO2 inside their leaves."

Leakey said that further research is needed to determine how crops grown in developing regions of the world will respond to higher levels of atmospheric CO2.

"It's important that we start to do these experiments in tropical climates with tropical soils, because that's just a terrible gap in our knowledge, given that that's where food security is already the biggest issue.”

The researchers note the current study contributed “more than tenfold more data regarding both the zinc and iron content of the edible portions of crops grown under FACE conditions" than available from previous studies.

Lead author Samuel Myers, research scientist in the Department of Environmental Health at HSPH, said examining how rising CO2 levels affect nutrition is bound to yield further surprising results.

“This study is the first to resolve the question of whether rising CO2 concentrations — which have been increasing steadily since the Industrial Revolution — threaten human nutrition,” he said in an interview with the Harvard Gazette.

“Humanity is conducting a global experiment by rapidly altering the environmental conditions on the only habitable planet we know. As this experiment unfolds, there will undoubtedly be many surprises. Finding out that rising CO2 threatens human nutrition is one such surprise,” he said.

Image 2 (below): Free Air Concentration Enrichment (FACE) systems, like this one at the University of Illinois, allow researchers to simulate future atmospheric conditions to determine their effects on plants. Credit: Don Hamerman